The present invention relates generally to a rollover valve for use in a vehicle fuel tank.
Vehicle fuel tanks employ vent valves as part of evaporative emissions control systems in order to reduce the fuel vapors released from the fuel tank into the atmosphere. One valve used in such systems is commonly called a rollover valve. The rollover valve mounts in the top of the tank and allows fuel vapors to be carried through a vapor passage to an evaporative emissions canister. These fuel vapors can then be burned in the vehicle engine rather than released into the atmosphere. The valve is called a rollover valve because, should the vehicle be in a situation where it is upside down, a float in the valve will block the vapor passage to the evaporative emissions canister. This, then, prevents liquid fuel from flowing out of the tank through the vapor passage.
Fuel tank assemblies may also include fluid limit vent valves, which act in concert with a rollover valve during vehicle refueling. The two valves help reduce the amount of vapors emitted from the fuel tank while it is being refueled. As the tank is filled with liquid fuel, the liquid fuel will reach a level where the fluid limit vent valve closes, so it no longer allows for venting of vapors through it. Once the fluid limit vent valve closes, the remaining fuel vapors in the tank are exhausted through the rollover valve. Additional fuel can be added with the refueling nozzle after the initial shut-off, with the volume dispensed dependant on the type of rollover valve used. The amount of fuel vapor venting is a balance between overfilling the fuel tank and not providing enough venting capabilities, which can lead to a spit-back condition.
This balance may be achieved using valves that start with a small orifice at low pressures and open to a larger orifice when a second stage of a rollover valve opens due to higher tank pressures. This type of arrangement requires balancing of opening pressures for valves from tank system to tank system, and so can be rather difficult. So this is not always a desirable solution.
Another way to vent the fuel tank during refueling involves the use of several valves. Such fuel tank systems have a fluid limit vent valve and two separate rollover valves. The first rollover valve is buried in fuel following the additional fuel added after the initial shut-off (which, as discussed above, caused the fluid limit vent valve to close). The second rollover valve is located to then vent the fuel vapors to the evaporative emission canister. This solution is not particularly desirable, however, because it requires the use of an extra rollover valve to accomplish satisfactory venting capabilities.